Anti-emissions compression piston ring

ABSTRACT

A U-shaped cross section piston ring mounted about the top of an internal combustion engine piston with a lower leg of the ring received in a circumferential groove spaced from the piston head and an upper leg of the ring overlying the top of the piston or received in a circumferential ledge recessed in the margin of the piston head. An important feature resides in that the surface area of the piston head about the inner edge of the upper leg of the ring extends radially inwardly away from the lower surface of the ring upper leg so that expanding gases from within the ring are freely directed to the hotter central portion of the piston head and positively away from the cylinder wall.

United States Patent Prasse Aug. 26, 1975 ANTI-EMISSIONS COMPRESSION PISTON 2,761,748 9/1956 Marien 277/161 RING 2,800,376 7/1957 Traupmann et a1. 92/194 [75] Inventor: Herbert F. Prasse, St. Louis, Mo. FOREIGN PATENTS OR APPLICATIONS 13,513 7/1934 Australia 92/246 [73] Assigne Ramsey Corporation, St Lou1s, Mo. 448,864 5/1949 Italy u [22] Filed: May 21, 1973 264,994 2/1950 Switzerland 277/178 21 A l. N 362002 1 pp 0 Primary Examiner-Irwin C. Cohen Related Application Data Attorney, Agent, or FirmI-Iill, Gross, Simpson, Van [63] Continuationin-part of Ser. Nos. 815,653, April 14, Santen, Steadman, Chiara & Simpson 1969, abandoned, and Ser. No. 183,201, Sept. 23,

71 b d 19 57 ABSTRACT [52] US. Cl. 92/182; 92/ 193; 92/200; A U-shaped cross section piston ring mounted about 277/ 168; 277/178 the top of an internal combustion engine piston with a [51] Int. Cl. F16j 1/00; F16j 9/06; F16j 9/08 lower leg of the ring received in a circumferential [58] Field of Search 92/181, 182, 193, 184, groove spaced from the piston head and an upper leg 92/200, 185, 246, 203, 198; 123/193 P; of the ring overlying the top of the piston or received 277/174, 170, 178, 206, 168 160, 161 in a circumferential ledge recessed in the margin of the piston head. An important feature resides in that [56] References Cited the surface area of the piston head about the inner UNITED STATES PATENTS edge of the upper leg of the ring extends radially inl 364 005 121920 Sullivan 92,246 wardly away from the lower surface of the ring upper l450l34 3/l923 cisskimji X leg so that expanding gases from within the ring are 4 5/1923 Day 123/193 p freely directed to the hotter central portion of the pis- 1,710,01 l 4/1929 Burnett... 92/182 ton head and positively away from the cylinder wall. 2,074,581 3 1937 Frye 277/178 x 2,367,030 1/1945 Jessup 277/178 12 Clalms, 6 Drawing Figures ANTI-EMISSIONS COB/IPRESSION PISTON RING PRIOR APPLICATIONS This application is a continuation in-part of my application Ser. No. 815,653 filed Apr. 14, 1969, now abandoned, and copending application Ser. No. 183,201 filed Sept. 23, 1971 which was copending with said abandoned application.

FIELD OF THE INVENTION The present invention relates to internal combustion engine piston and piston ring combination, and more importantly to an anti-emissions arrangement of the piston ring and the piston.

PRIOR ART Recent developments in internal combustion engine technology have emphasized the reduction of engine emissions. Such emissions may be caused to a great extent by failure to burn all of the fuel injected into the engine cylinders. Exhaust of unburned hydrocarbons may greatly contribute to air pollution.

In a conventional piston and piston ring design, the upper compression piston ring is positioned in a ring groove spaced axially from the top of the piston. This creates a circumferential crevice between the outer diameter of the piston and the cylinder wall in the area above the upper compression ring. To the extent that the upper compression ring does not fit snugly with the top radial wall of the ring groove, that area also forms a crevice. As the piston rises in the cylinder during the compression stroke, fuel can condense along the cylinder wall and be thrust into the above-mentioned crevices. Because of the small space involved, combustion may not take place in these crevices, allowing the formation of undesired emission products.

Attempts have been made to correct this by placing the upper compression ring groove as close to the top of the piston as possible. However, placement of a conventional ring groove is limited by the necessity of not weakening the top of the piston. If the conventional ring groove is placed too close to the top of the piston, the groove may result in a peripheral weak point at the top of the piston. In addition, the top of the piston is the most hostile environment for a piston ring. That area is subjected to the greatest heat and pressure and extreme wear would be encountered utilizing a conventional ring in that area.

SUMMARY My invention provides for the virtual elimination, and at least great reduction in emissions from internal combustion engine cylinders by avoiding condensation of unburned fuel along the cylinder wall. For this purpose an improved piston ring arrangement is provided wherein a U-shaped cross section piston ring with axially spaced apart legs has the web section which spans the legs in engagement with the cylinder wall, and the upper leg so located with respect to the top or crown of the piston as to assure that expanding gases from behind the ring are direction toward the hotter center area of the piston head in the vicinity of the vertical axis of the piston. The arrangement is such that a lower A ripheral ledge recessed in the top of the piston, and in either instance with the piston surface radially inwardly from the upper leg of the ring extending generally radially inwardly in a manner to direct expanding gases from behind the ring toward the center area over the piston head.

In a preferred embodiment, an expander may be used in the piston ring channel to aid in expanding the ring periphery into engagement with the cylinder wall. The ring may also utilize the expansive force created during the power stroke as an aid in both circumferential and axial sealing. The peripheral portion of the ring seals against the cylinder wall while the radial legs are sealed against radial walls of the groove or ledge.

It is therefore an object of this invention to provide a new antiemissions piston ring and piston arrangement.

Another object of the invention is to provide a new and improved piston and piston ring arrangement which will efficiently avoid condensing of unburned fuel on the cylinder wall.

A further object of the invention is to provide a new and improved method of controlling emissions from an internal combustion engine.

Still another object of the invention is to provide new and improved means for efficient emissions control in internal combustion engines.

Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawing although variations and modifications may be effected without departing from the spirit and scope of the novel concepts embodied in the disclosure, and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary cross-sectional view of an internal combusion engine piston received in a cylinder bore equipped with the anti-emissions ring of this invention;

FIG. 2 is a fragmentary sectional plan view taken substantially along the line II-Il of FIG. 1;

FIG. 3 is a fragmentary enlarged cross-sectional view showing an enlargement of that portion of FIG. 1 within the circle III and showing the relationship during the power and compression strokes;

FIG. 4 is a view similar to FIG. 3 during the exhaust stroke;

FIG. 5 is a view similar to FIG. 4 during the'intake stroke; and

FIG. 6 is a view similar to FIG. 3 illustrating another embodiment of this invention.

DESCRIPTION OF THE PREFERRED I EMBODIMENTS FIG. 1 is a fragmentary cross-sectional view of a piston 10 received in the bore 11 of a cylinder 12. The piston head includes conventional piston ring grooves l3, l4 and 15. Compression rings 16 and 17 are positioned in the ring grooves 13 and 14 and a combination circumferential spacer-expander and dual rail oil control ring 18 is positioned in the ring groove 15. The ring groove 15 has an oil drainage bore 19 therein adapted to drain oil scraped by the oil control ring 18.

As is conventional, the top compression ring groove 13 is spaced axially below the top or head 20 of the piston 10. Thus, a large area crevice 21 is provided between the. wall 22 of the cylinder bore 1 1 and the outer diameter 23 of the piston If) above the ring 16. During thecompression and power strokes, when the ring 16 is pressed against the bottom radial wall 24 of the ring groove 13, an additional crevice area is provided in the area 25 between the top radial wall 26 of the groove 13 and the top of the ring 16 and the areas between the back wall 27 of the groove 13 and the back of the ring 16. In a conventional arrangement, during compression fuel injected into the cylinder would be forced into the crevices 21 and 25. In most internal combustion engines, the cylinder wall 22 is cooler than either the piston or the interior of the cylinder bore 11. This allows the injected fuel vapor to condense along the cylinder wall. In a conventional arrangement the condensed fuel vapor can substantially fill the crevices 21, 25. These crevices may be too small to support combustion of the condensed fuel therein during the power stroke of the piston. This would produce a quantity of unburned fuel during each cycle of the engine which would then form pollutant emissions which escape the engine through the exhaust. In addition, because the top compression ring 16 never reaches the top of the cylinder bore, carbon deposits can build up on the cylinder wall 22 and in the top ring groove 13 in a conventional arrangement. These carbon deposits adversely affect the operation of the engine and can, of themselves, in a conventional arrangement add to the pollutant emissions of versely arched web portion or section 30a connecting the legs 31 and 32 at the outer periphery thereof.

The ring 30 may be either cast or rolled. The web section 30a may be slightly rounded in an axially outward direction and may have a hard-faced coating on the outer'periphery thereof to increase the life of the 'ringand reduce scuffing. The outer diameter of the web 30a is adapted to contact thecylinder wall 22 in circumferential engagement therewith thereby preventing the formation of carbon deposits and condensed fuel buildup in the crevices 21 and 25.

The U-shaped cross section of the ring 30 allows the ring to be placed about the top of the piston while atthe same time providing for a more complete sealing than can be achieved with'a solid ring.

As best illustrated in FIG. 3, the ring 30 is located at the head of thepiston 10 having the upper radial leg 31 lying in substantial alignment with the head 20 and the lower radial leg 32 received in a radial ring groove 33 spaced axially from the head 20 of the piston 10.

The ring is split having circumferential ends 30a.

The'ring is designed tobe installed in a cylinder bore in a circumferentially compressed condition where it 'wil] expansibly engage the cylinder wall 22. Preferably the groove 33 has an axial height or width slightly greater than 'the axial height 'or thickness of the leg lower 32 so as to allow free vertical movement of the leg therein. Further, the groove 33 has a radial depth sufficient to allow the leg 32 to be received therein in a non-bottoming radial relation.

While the groove 33 may be located axially below the head 20 of the piston 10 by a distance which will allow the upper leg 31 to overlie the head 20, it is preferable to have it dimensioned so that the top radial wall 34 of the upper leg 31 is generally coplanar with the head 20 of the piston 10. To this end a peripheral ledge 35 is recessed in the margin of the head 20 of the piston 10 to receive the leg 31. In order to assure generally radial free flow displacement of gases between the underside surface 31a of the upper ring leg 31 and the piston head 20, as indicated by directional arrows in FIG. 2, the ledge 35 has an annular generally radially inwardly slanting ramp surface 36 which extends from a radial wall surface 37 underlying the leg surface 31a. This surface 37 extends radially into the piston 10, a width dimension greater than the operating radial extent of the leg 31 from the side perimeter 23 of the piston 10. Thus, the leg 31 of the ring is non-bottoming against the ramp 36, and an efficient gap 38 is provided between an inner diameter edge 39 of the leg 31 and the ramp 36.

A second, generally rabbet groove ledge 40 may be recessed in the outer margin of the ledge 35 and provides a radial wall 41 and an axial wall surface 42. The ledge 40 is substantially axially narrower than the width of the ring 30 and provides a seat for an equally narrow expansion ring 43 which acts against the upper portion of the inner periphery 44 of the web section 30a of the ring 30. The expansion spring 43 is illustrated as being of the wave type wherein the inner diameter of the convolutions bottom and thrust under compression against the wall 42 of the groove 40 and the outer diameter convolutions bottom and thrust under compression against the inner diameter 44 of the web 30a of the ring 30, thus circumferentially expanding the ring into stable, sliding tight sealing engagement with the wall 22 of the cylinder bore 1 1. Because it is quite riarrow relative to the axially greater width of the ring 30, the expander 43 even though of metal does not interfere frictionally with axial relative recipricating movements of the ring 30 and the piston 10. The outer diameter of the web 30a has a wear and scuff resistant coating 45 thereon.

In its U-shaped cross section construction the ring 30 is dimensioned to cooperate with surfaces of the piston in the groove 33 and the ledge 35 to aid efficiently in sealing the firing combustion chamber zone 46 within the cylinder bore 11 above the head 20 of the piston 10. FIG. 3 illustrates the sealing action of the ring 30 during the power and compression strokes. The arrowed lines illustrate the effect of the expanding combusted gases during the power stroke, as well as the compressed vapors during the compression stroke. The axial depth of the ledge 35 is preferably great enough so that the axial force of the gases illustrated by the arrowed lines 47 on the top leg 31 of the ring 30 will not cause the leg 31 to be deflected into sealing contact with the radial wall 37 of the ledge. Therefore, some of the pressurized gases will pass through the gap 38 past the edge 39 of the leg 31 and down the ramp 36 into the space 48 between the piston 10 and the inner diameter 44 of the web section 30a of the ring. These gases will act in concert with the expander spring 43 to press the ring radially outwardly against the cylinder wall 22. In addition, the gases will act against the top surface 32b of the bottom leg 32 to force this leg into sealing engagement with a bottom radial wall surface 50 of the groove 33. Because of the heat of the piston 10, fuel vapor will not condense interiorly of the ring during the compression stroke to the same extent that it would condense upon contact with the cold cylinder wall 22.

During both the compression and power stokes, the fuel vapor is therefore contained within the area above the top 20 of the piston except for that small amount of vapor which is allowed to act against the radially inner side of the ring 30.

Because the piston ring 30 is located about the top of the piston 10, and because it uses both the compressed and combusted gases to aid in sealing against the cylinder wall, sealing is more effective than in a conventional top compression ring such as the ring 16. The gases do not have as far to travel before exerting their sealing pressure on the ring, thus reducing the time lapse between combustion and sealing. Therefore, the amount of blowby past the ring is minimized.

FIG. 4 illustrates the gas flow and ring positioning during the exhaust stroke. Due to the upward movement of the piston 10 during the exhaust stroke, as well as due to the existence of pressured gases in the cavity provided by the space 48, a bottom radial wall surface 32a of the leg 32 of the ring 30 is retained in sealing contact with the bottom wall 50 of the groove 33. Because the majority of the fuel vapor in the space 48 is not condensed due to the heat of the piston 10, that vapor, assuming it is not combusted, is free to escape the space 48 through the gap 38 in view of the decrease in pressure in the firing zone 46. The vapor thus will combine at an early stage with the hot combustion gases and be combusted. It can thus be seen that the area below the ring is sealed from the firing zone 46 due to the sealing contact between the outer periphery of the ring 30 and the cylinder wall 22 and the sealing engagement between the bottom leg surface 32 and the bottom radial wall 50 of the groove 33 during the exhaust stroke. However, because the vapor does not condense in the space 48, it can combust therein during the power stroke and the gases thus produced will escape during the exhaust stroke. Any uncombusted vapor that returns from within the ring 30 as indicated by the directional arrows in FIG. 4 is efficiently directed toward the axis of the piston 10 over the top 20, which is the hottest region within the cylinder, without any tendency to move toward or be deflected toward the cylinder wall 22, as has been common in prior arrangements.

FIG. 5 illustrates the position of the ring during the intake stroke. At this point, the piston 10 is moving downwardly to draw fuel vapor into the combustion zone 46. Insufficient gas will remain in the intraring space 48 to press the bottom leg 32 of the ring 30 against the bottom wall 50 of the groove 33. Downward movement of the piston 10 coupled with the inertia of the ring and the presence of a reduced pressure area in the combustion space 46 will combine to lift the ring 30 with respect to the piston 10 until a top surface 32b of the leg 32 has contacted the top wall 49 of the groove 33 and is sealed thereagainst. Whatever vapor remains in the space 48 will be allowed to escape from the ex panded space between the surfaces 31a and 37 and through the gap 38 and is directed generally radially inwardly, as shown by directional arrows to recombine with the vapor in the combustion zone 46.

Therefore, the ring 30 seals the combustion zone 46 not only during the power stroke, but also during the exhaust intake and compression strokes. Further, the

ring 30 acts to eliminate or at least greatly minimize uncombusted fuel vapors throughout the firing cycle of the engine. The ring 30 acts as both a compression ring and as an emissions control ring.

FIG. 6 illustrates a modification involving the ring 30, and wherein the piston 10' is provided with a single ledge which terminates in a radially outer axially extending wall surface 61 which has an outer diameter less than the outer diameter 62 of the remainder of the piston 10. The wall surface 61 extends from the radial wall surface 63 of the ledge 60 to the groove 33'. An elastomeric expander 65 is provided between the wall surface 61 and the inner diameter of the ring 30. The elastomeric expander is dimensioned to fill the majority of the area between the wall 61 and the inner diameter of the ring thereby providing blockage in the axial direction around the inner periphery of the ring. This further reduces the crevice area in the interior of the ring. Thus, the fuel vapors are restricted to the area 66 below the top leg 31 of the ring 30 and above the wall surface 63 of the ledge 60 and the elastomer expander 65.

Because of the ability of the gases in the combustion area 46 to act against the inner edge 39 of the top leg 31 of the ring 30 at the flow gap 38 and against a portion of the inner diameter of the web 30a, sealing will be accomplished in the same manner as in the prior embodiment with the'exception that the gases will not act against the bottom leg 32 of the ring except through gas pressure compression and deflection of the elastomeric expander 65. Also, it may be noted, that because of its elastic yieldability, the elastomeric expander 65 permits the ring 30 to, in effect, float or reciprocate relative to the piston 10 to the limited extent permitted by the differential in thickness of the lower ring leg 32 relative to the axial width of the groove 33, whereby expansion of the space 60 between the upper ring leg 31 and the ledge surface 63 during the intake stroke is effected for efficient evacuation of any possible unburned fuel vapor in that space for comingling with the indrawn fuel.

As has been mentioned, the ring of this invention may be a cast ring or may be rolled into its U-shaped cross section. The reduced thickness of the ring in comparison to standard compression rings allows greater response of the ring to engine operating conditionsfBecause of the extreme heat encountered at the top of the piston, normal compression rings encounter extreme wear. For this reason, the rings of this invention are preferably flame-spray coated with molybdenum or the like metals or plasma-coated with refractory alloy metals as is taught in my US. Pat. No. 3,539,192 the teachings of which are expressly incorporated herein by reference.

It can therefore be seen that my invention provides for a new piston ring and piston combination having a new and improved relationship to reduce blowby and carbon formation while effectively minimizing engine emissions by preventing escape of unburned hydrocarbons. Thereby the present invention solves a problem of substantial magnitude that has heretofore existed by reason of condensation of fuel vapor against the cooler cylinder wall and entrapment in crevice spaces between the piston and the cylinder wall. According to the present invention possibly unburned vapors are efficiently directed toward the center of the combustion zone.

Although the teachings of my invention have herein been discussed with reference to specific theories and embodiments, it will be understood that these are by way of illustration only and that variations and modifications may be effected without departing from the spirit and scope of the novel concepts of this invention.

I claim as my invention:

1. The internal combustion engine piston and piston ring combination comprising:

a piston having a head;

said piston having a circumferential ring groove with top and bottom radial wall surfaces adjacently axially spaced from said head;

an emissions control ring having axially spaced radially inwardly directed upper and lower legs interconnected by a radially outer peripheral web section;

said web section being adapted to ride against the wall of a cylinder in which the piston is received reciprocably;

said ring being positioned around the outer periphery of the piston at said head with said lower leg extending into said groove;

said upper leg overlying said head in axial clearance relation defining a space between an underside surface of said upper leg and a radially extending upwardly facing surface area of the piston head underlying said underside surface and extending radially inwardly beyond the inner edge of said upper leg;

the surface of said head radially inwardly about said underlying surface area of the head extending generally radially inwardly as an extension from said surface area and away from said underside surface of said upper leg;

said lower ring leg and said groove being of differential axial width so that said lower leg has a limited range of axial permissible movement in said groove, the range of permissible movement of the lower leg being less than the axial width of the clearance space between said upper leg and said underlying piston head area, whereby the ring is permitted to have a limited range of reciprocating movement relative to the piston head, with consequent enlargement of said clearance in one phase ofa firing cycle involving the piston in the cylinder; and a metal expansion spring acting in said space between said web and said piston and having its upper edge substantially aligned with said underlying surface area to thrust the emissions control ring against the wall of a cylinder within which the piston is received, said ring being substantially narrower than said web to avoid frictional interference with reciprocable movements of the control ring; whereby during'firing cycles involving said piston in a cylinder, gases and vapors may move freely into and out of said clearance past the inner edge of said upper leg, and on moving out of said clearance past said inner edge of said upper leg the vapors and gases are directed toward the center over said piston head in a combustion zone in the cylinder and positively away from the cylinder wall engaged by the ring.

2. An internal combustion engine piston and piston ring combination comprising:

a piston having a head;

said piston having a circumferential ring groove with top and bottom radial wall surfaces adjacently axially spaced from said head;

an emissions control ring having axially spaced radially inwardly directed upper and lower legs interconnected by a radially outer peripheral web section;

said web section being adapted to ride against the wall of a cylinder in which the piston is received reciprocably;

said ring being positioned around the outer periphery of the piston at said head with said lower leg extending into said groove;

said upper leg overlying said head in axial clearance relation defining a space between an underside surface of said upper leg and a radially extending upwardly facing surface area of the piston head underlying said underside surface and extending radially inwardly beyond the inner edge of said upper leg;

the surface of said head radially inwardly about said underlying surface area of the head extending generally radially inwardly as an extension from said surface area and away from said underside surface of said upper leg;

and an expansion ring substantially narrower than said web acting between said web and the piston and having its upper edge substantially aligned with said underlying surface area to thrust the ring radially outwardly into engagement with a cylinder wall; whereby during firing cycles involving said piston in a cylinder, gases and vapors may move freely into and out of said clearance past the inner edge of said upper leg, and on moving out of said clearance past said inner edge of said upper leg the vapors and gases are directed toward the center over said piston head in a combustion zone in the cylinder and positively away from the cylinder wall engaged by the ring.

3. A combination according to claim 2, wherein said surface of the piston head radially inwardly about the underlying surface area comprises an annular surface portion extending on an oblique slant generally radially inwardly from said underlying area.

4. A combination according to claim 2, wherein said underlying area of the piston head comprises a ledge recessed in the margin of the piston head, and said surface of the head radially inwardly about the underlying surface area comprises an oblique ramp extending generally radially inwardly away from said underlying surface area and the inner edge of said upper leg of the ring.

5. In a combination according to claim 2, wherein said lower ring leg and said groove are of differential axial width so that said lower leg has a limited range of axial permissible movement in said groove, the range of permissible movement of the lower leg being less than the axial width of the clearance space between said upper leg and said underlying piston head area, whereby the ring is permitted to have a limited range of reciprocating movement relative to the piston head, with consequent enlargement of said clearance in one phase of a firing cycle involving the piston in the cylinder.

6. A combination according to claim 5, including a space between the web section of the ring and a perimeter area of the piston whereby pressure from within the cylinder over the piston head may be effective through said clearance and said space on said lower leg to thrust the lower leg sealingly against a lower surface within said groove.

7. A combination according to claim 2, wherein said piston has a rabbet groove ledge recessed below said underlying surface area, and said expansion ring is seated in said groove ledge.

8. A piston and piston ring combination for use in a cylinder of an internal combustion engine, comprising:

a piston having a top face including an upwardly facing annular marginal surface;

a radial groove with radial wall surfaces circumferentially in the piston axially spaced from said marginal surface;

an emissions control ring having a U-shaped cross section with upper and lower radially directed legs interconnected at the radially outer periphery thereof by a web portion; the upper leg of said control ring being of substantial width but being narrower than said marginal surface and being located over said marginal surface with axial and radial clearance between the upper leg and said marginal surface; radial clearance between the inner diameter of said web portion and the outer diameter of the piston intermediate said marginal surface and the groove;

said lower leg being freely received with an axial clearance in said groove and which clearance of the lower leg is less than the axial clearance between the bottom surface of the upper leg and said marginal surface;

the bottom suface of the lower leg sealingly engaging a bottom radial surface defining the groove during the compression and combustion strokes involving the piston;

an annular surface area of the piston head leading as an extension generally radially inwardly away from said marginal surface and the clearance between the upper leg and said marginal surface whereby gases from between the upper leg of the control ring and said marginal surface are vented directly toward the cylinder axis above said piston head and away from the wall of the cylinder;

and a depressed ledge in the radially outer portion of said marginal surface and substantially narrower than said marginal surface and shallower in axial depth than the width of said web, and a narrow metal expansion spring seated on said ledge and thrusting against said web portion to push the web portion against the cylinder wall.

9. A combination according to claim 8, wherein said marginal surface comprises a recessed ledge in the piston head top face, and said surface area comprises a ramp slanting from said marginal surface generally radially inwardly toward said axis.

10. A piston and piston ring combination for use in a cylinder of an internal combustion engine, comprisa piston having a top face including an upwardly facing annular marginal surface;

a radial groove with radial wall surfaces circumferentially in the piston axially spaced from said marginal surface;

an emissions control ring having a U-shaped cross section with upper and lower radially directed legs vinterconnected at the, radially outer periphery thereof by alweb portion;

.the upper. leg of said control ring being of substantial width but being narrower than said marginal surface and being located over said marginal surface with axial and'radial clearance between the upper leg and said marginal surface;

radial clearance between the inner diameter of said web portion and the outer diameter of the piston intermediate said marginal surface and the groove;

said lower leg being freely received with an axial clearance in said groove and which clearance of the lower leg is less than the axial clearance between the bottom surface of the upper leg and said marginal surface;

the bottom surface of the lower leg sealingly engaging a bottom radial surface defining the groove during the compression and combustion strokes involving the piston;

an annular surface area of the piston head leading as an extension generally radially inwardly away from said marginal surface and the clearance between the upper leg and said marginal surface whereby gases from between the upper leg of the control ring and said marginal surface are vented directly toward the cylinder axis above said piston head and away from the wall of the cylinder;

and an elastomer expansion spring in said radial clearance between the inner diameter of said web portion and the outer diameter of the piston, said expansion spring being axially elastic to permit axial reciprocation of the control ring relative to the piston and having its top edge substantially aligned with said marginal surface.

11. A combination according to claim 10, wherein said marginal surface comprises a recessed ledge in the piston head top face, and said surface area comprises a ramp slanting from said marginal surface generally radially inwardly toward said axis.

12. An internal combustion engine piston and piston ring combination, comprising:

a piston having a top;

said piston having a circumferential ring groove with top and bottom radial walls closely axially spaced from the top of the piston;

an emissions control ring having axially spaced radially directed legs of substantial width interconnected by an outer peripheral web portion adapted to ride against the wall of a cylinder in which the piston is received;

said ring having its lower leg received in said groove and the groove being axially wider than the thickness of said lower leg;

said ring having its upper leg overlying the margin of the piston top and spaced above said margin a greater distance than the total clearance between said lower leg and said groove;

the inner diameter of said ring web portion being greater than the diameter of the piston between said legs;

a rabbet ledge recessed in said margin and said piston diameter and of narrower radial width than the width of said upper leg and of substantially less axial depth than the width of said web portion; and

a metal expansion wave spring received in said ledge and thrusting said web portion toward the cylinder wall;

1 l 1 2 said expansion ring permitting compressed gases to tom of said groove and said expansion ring also act through the Space between Said upper leg and permitting reciprocations of the control ring relasaid margin and through the expansion ring and the space between said web portion and said piston on said lower leg to drive it sealingly against the bot- 5 tive to the piston. 

1. The internal combustion engine piston and piston ring combination comprising: a piston having a head; said piston having a circumferential ring groove with top and bottom radial wall surfaces adjacently axially spaced from said head; an emissions control ring having axially spaced radially inwardly directed upper and lower legs interconnected by a radially outer peripheral web section; said web section being adapted to ride against the wall of a cylinder in which the piston is received reciprocably; said ring being positioned around the outer periphery of the piston at said head with said lower leg extending into said groove; said upper leg overlying said head in axial clearance relation defining a space between an underside surface of said upper leg and a radially extending upwardly facing surface area of the piston head underlying said underside surface and extending radially inwardly beyond the inner edge of said upper leg; the surface of said head radially inwardly about said underlying surface area of the head extending generally radially inwardly as an extension from said surface area and away from said underside surface of said upper leg; said lower ring leg and said groove being of differential axial width so that said lower leg has a limited range of axial permissible movement in said groove, the range of permissible movement of the lower leg being less than the axial width of the clearance space between said upper leg and said underlying piston head area, whereby the ring is permitted to have A limited range of reciprocating movement relative to the piston head, with consequent enlargement of said clearance in one phase of a firing cycle involving the piston in the cylinder; and a metal expansion spring acting in said space between said web and said piston and having its upper edge substantially aligned with said underlying surface area to thrust the emissions control ring against the wall of a cylinder within which the piston is received, said ring being substantially narrower than said web to aVoid frictional interference with reciprocable movements of the control ring; whereby during firing cycles involving said piston in a cylinder, gases and vapors may move freely into and out of said clearance past the inner edge of said upper leg, and on moving out of said clearance past said inner edge of said upper leg the vapors and gases are directed toward the center over said piston head in a combustion zone in the cylinder and positively away from the cylinder wall engaged by the ring.
 2. An internal combustion engine piston and piston ring combination comprising: a piston having a head; said piston having a circumferential ring groove with top and bottom radial wall surfaces adjacently axially spaced from said head; an emissions control ring having axially spaced radially inwardly directed upper and lower legs interconnected by a radially outer peripheral web section; said web section being adapted to ride against the wall of a cylinder in which the piston is received reciprocably; said ring being positioned around the outer periphery of the piston at said head with said lower leg extending into said groove; said upper leg overlying said head in axial clearance relation defining a space between an underside surface of said upper leg and a radially extending upwardly facing surface area of the piston head underlying said underside surface and extending radially inwardly beyond the inner edge of said upper leg; the surface of said head radially inwardly about said underlying surface area of the head extending generally radially inwardly as an extension from said surface area and away from said underside surface of said upper leg; and an expansion ring substantially narrower than said web acting between said web and the piston and having its upper edge substantially aligned with said underlying surface area to thrust the ring radially outwardly into engagement with a cylinder wall; whereby during firing cycles involving said piston in a cylinder, gases and vapors may move freely into and out of said clearance past the inner edge of said upper leg, and on moving out of said clearance past said inner edge of said upper leg the vapors and gases are directed toward the center over said piston head in a combustion zone in the cylinder and positively away from the cylinder wall engaged by the ring.
 3. A combination according to claim 2, wherein said surface of the piston head radially inwardly about the underlying surface area comprises an annular surface portion extending on an oblique slant generally radially inwardly from said underlying area.
 4. A combination according to claim 2, wherein said underlying area of the piston head comprises a ledge recessed in the margin of the piston head, and said surface of the head radially inwardly about the underlying surface area comprises an oblique ramp extending generally radially inwardly away from said underlying surface area and the inner edge of said upper leg of the ring.
 5. In a combination according to claim 2, wherein said lower ring leg and said groove are of differential axial width so that said lower leg has a limited range of axial permissible movement in said groove, the range of permissible movement of the lower leg being less than the axial width of the clearance space between said upper leg and said underlying piston head area, whereby the ring is permitted to have a limited range of reciprocating movement relative to the piston head, with conseqUent enlargement of said clearance in one phase of a firing cycle involving the piston in the cylinder.
 6. A combination according to claim 5, including a space between the web section of the ring and a perimeter area of the piston whereby pressure from within the cylinder over the piston head may be effective through said clearance and said space on said lower leg to thrust the lower leg sealingly against a lower surface within said groove.
 7. A combination according to claim 2, wherein said piston has a rabbet groove ledge recessed below said underlying surface area, and said expansion ring is seated in said groove ledge.
 8. A piston and piston ring combination for use in a cylinder of an internal combustion engine, comprising: a piston having a top face including an upwardly facing annular marginal surface; a radial groove with radial wall surfaces circumferentially in the piston axially spaced from said marginal surface; an emissions control ring having a U-shaped cross section with upper and lower radially directed legs interconnected at the radially outer periphery thereof by a web portion; the upper leg of said control ring being of substantial width but being narrower than said marginal surface and being located over said marginal surface with axial and radial clearance between the upper leg and said marginal surface; radial clearance between the inner diameter of said web portion and the outer diameter of the piston intermediate said marginal surface and the groove; said lower leg being freely received with an axial clearance in said groove and which clearance of the lower leg is less than the axial clearance between the bottom surface of the upper leg and said marginal surface; the bottom suface of the lower leg sealingly engaging a bottom radial surface defining the groove during the compression and combustion strokes involving the piston; an annular surface area of the piston head leading as an extension generally radially inwardly away from said marginal surface and the clearance between the upper leg and said marginal surface whereby gases from between the upper leg of the control ring and said marginal surface are vented directly toward the cylinder axis above said piston head and away from the wall of the cylinder; and a depressed ledge in the radially outer portion of said marginal surface and substantially narrower than said marginal surface and shallower in axial depth than the width of said web, and a narrow metal expansion spring seated on said ledge and thrusting against said web portion to push the web portion against the cylinder wall.
 9. A combination according to claim 8, wherein said marginal surface comprises a recessed ledge in the piston head top face, and said surface area comprises a ramp slanting from said marginal surface generally radially inwardly toward said axis.
 10. A piston and piston ring combination for use in a cylinder of an internal combustion engine, comprising: a piston having a top face including an upwardly facing annular marginal surface; a radial groove with radial wall surfaces circumferentially in the piston axially spaced from said marginal surface; an emissions control ring having a U-shaped cross section with upper and lower radially directed legs interconnected at the radially outer periphery thereof by a web portion; the upper leg of said control ring being of substantial width but being narrower than said marginal surface and being located over said marginal surface with axial and radial clearance between the upper leg and said marginal surface; radial clearance between the inner diameter of said web portion and the outer diameter of the piston intermediate said marginal surface and the groove; said lower leg being freely received with an axial clearance in said groove and which clearance of the lower leg is less than the axial clearance between the bottom surface of the upper leg and said marginaL surface; the bottom surface of the lower leg sealingly engaging a bottom radial surface defining the groove during the compression and combustion strokes involving the piston; an annular surface area of the piston head leading as an extension generally radially inwardly away from said marginal surface and the clearance between the upper leg and said marginal surface whereby gases from between the upper leg of the control ring and said marginal surface are vented directly toward the cylinder axis above said piston head and away from the wall of the cylinder; and an elastomer expansion spring in said radial clearance between the inner diameter of said web portion and the outer diameter of the piston, said expansion spring being axially elastic to permit axial reciprocation of the control ring relative to the piston and having its top edge substantially aligned with said marginal surface.
 11. A combination according to claim 10, wherein said marginal surface comprises a recessed ledge in the piston head top face, and said surface area comprises a ramp slanting from said marginal surface generally radially inwardly toward said axis.
 12. An internal combustion engine piston and piston ring combination, comprising: a piston having a top; said piston having a circumferential ring groove with top and bottom radial walls closely axially spaced from the top of the piston; an emissions control ring having axially spaced radially directed legs of substantial width interconnected by an outer peripheral web portion adapted to ride against the wall of a cylinder in which the piston is received; said ring having its lower leg received in said groove and the groove being axially wider than the thickness of said lower leg; said ring having its upper leg overlying the margin of the piston top and spaced above said margin a greater distance than the total clearance between said lower leg and said groove; the inner diameter of said ring web portion being greater than the diameter of the piston between said legs; a rabbet ledge recessed in said margin and said piston diameter and of narrower radial width than the width of said upper leg and of substantially less axial depth than the width of said web portion; and a metal expansion wave spring received in said ledge and thrusting said web portion toward the cylinder wall; said expansion ring permitting compressed gases to act through the space between said upper leg and said margin and through the expansion ring and the space between said web portion and said piston on said lower leg to drive it sealingly against the bottom of said groove and said expansion ring also permitting reciprocations of the control ring relative to the piston. 